Design of microprocessor architecture enables the efficient handling of instructions to allow for smooth user experiences. Many hardware improvements have been implemented including the use of a re-order buffer (ROB) that can store instructions and register data. However, the ROB is a large structure and continual access of the ROB, especially for frequent checking of data dependency, is a slow and resource intensive process. As the ROB continues to increase in size to 64 or 128 entries, ROB associative search becomes a significant bottleneck for the clock frequency. To overcome this, subsequent implementations of microprocessor architecture has utilized a separate register known as a future file.
A future file holds a copy of speculative data that may be rapidly accessed upon further instructions, thereby eliminating the need to consistently access the ROB. However, future files continue to increase in size (e.g. 32 registers) with the increasing complexities of today's microprocessor architecture. Thus, accessing the future file has also become a resource intensive action, resulting in the loss of the advantages initially conferred by the development of a future file.
A parallel problem with conventional microprocessor architecture is the implementation of downstream reservation stations (RS) that receive all source operand data from the future file. The RS holds the source operand data, which requires large data width for each RS entry. Thus, processing of instructions and data through the RS becomes a resource intensive process as well.